Less sleep may have allowed humans to devote time to learning skills and forging social bonds, whereas deeper sleep may be critical for sharpening and enhancing cognitive abilities.

"Humans are a unique species and given the intuitive concept that our sleep is linked to how we think, feel and behave, I was less surprised and more excited about the findings that support the idea that sleep has played a part in the evolution of our species," Dr. David Samson, an evolutionary biologist at the university and a co-author of the study, told The Huffington Post.

The researchers compiled a database of sleep patterns among hundreds of mammals, including humans and 21 other primate species, such as chimpanzees and baboons. Then, the researchers conducted a statistical analysis of their data and found that humans are the shortest sleepers of all the primates, snoozing for an average of about seven hours a night. Most primates get between 14 and 17 hours of shut-eye.

The researchers concluded that humans are able to rest less because they get more rapid-eye-movement, or REM, sleep per hour than do other species. About 25 percent of our time sleeping is spent in this deeper, more relaxed mental state, compared to only 5 percent in other primates.

Scientists aren't sure why humans evolved to make the most of sleep. One hypothesis is that the advent of artificial light "tricked" our biological clocks into sleeping less, but the researchers think that a shift towards a shorter and more efficient snooze may be linked to humans sleeping on the ground instead of in trees, as our early human ancestors probably did.

"Certain prerequisites have to be met in one’s sleep environment to have deep sleep because when you are in it you are less easily aroused, and thus more vulnerable," Samson said.

"This vulnerability would have been life threatening in the wild, if not for early humans living in larger groups, controlling fire (which keeps you warm and repels predators small and large) and sleeping consistently on stable, terrestrial sleeping surfaces," he added. "All these elements working together could have removed previous barriers in attaining the kind of high quality sleep humans are characterized by today."